76 Equilibrium Studies of Ternary Systems Involving Some Selectedtransition Metal Ions, Triazoles and Aromatic Carboxylic Acids

Solution equilibria of the binary and ternary complex systems of the divalent transition metal ions CuII, NiII, ZnII, and CoII with 1,2,4-triazole (TRZ), 3-mercapto-1,2,4-triazole (TRZSH), and 3-amino-1,2,4-triazole (TRZAM) and aromatic carboxylic acids (phthalic, anthranilic, salicylic, and 5-sulfosalicylic acid) have been studied pH-metrically at (25.0 ± 0.1) oC, and a constant ionic strength I = 0.101…mol1…dm1’3 NaNO3 in an aqueous medium. The potentiometric titration curves show that binary and ternary complexes of these ligands are formed in solution. The stability constants of the different binary and ternary complexes formed were calculated on the basis of computer analysis of the titration data. The relative stability of the different ternary complex species is expressed in terms of 1 log K values and log X parameters. The effect of temperature of the medium on both the proton-ligand equilibria for TRZAM and phthalic acid and their metal-ligand equilibria with CuII, NiII, and CoII has been studied along with the corresponding thermodynamic parameters.